When camped at campgrounds with electricity included in the price.....I have always just used the electric portion of my water heater on the trailers I have owned, and save the propane for heating, cooking, etc.
Once you learn how to take 'Navy' showers, you shouldn't run out of hot water.
By this, I mean when you get in the shower, you turn the water on and wet yourself down good. You then turn the water off, usually by just pressing the button on most TT handheld showerheads that will stop the flow of water at the head. By stopping it at the showerhead, you won't have to adjust the cold/hot water taps each time.
You then soap up good, shampoo your hair, etc. Then turn the water on again and rinse off well.
By not leaving the water running the whole time you are in the shower, you aren't depleting your hot water tank nearly as much.......as well as not filling up your grey water tank with basically wasted water, which could have to be dumped depending on your length of stay.
It's just a personal preference thing, I guess......and can be a hard habit to break if you are used to taking long showers at your house, where hot water and drainage are of no concern.
P.S. When turning the water on/off at the handheld showerhead....make sure to turn the water back off at the hot and cold water taps when finished, so you won't leave the water pressure on at the head. Many of the showerheads have a built-in slow drip feature, that even when the water flow is shut off at the head, you will still know the water pressure is on by the water slowly dripping out of the head.